Complex binary digital sequences are useful in secure code generators, error correcting code generators, anti-jam circuits and other spread spectrum systems. In Generation of Binary Sequences With Controllable Complexity, IEEE Transactions on Information Theory, Vol. IT-17, No. 3, May 1971, by E. J. Groth, a concept was set forth for generating pseudo random bit strings with controllable complexity by means of combinations of shift registers of variable span combined with multipliers and modulo-two adders. Particular sequencing rules are set out in that paper which provide useful configurations for non-linear generators.
It is desirable in such systems to be able to vary the complexity of the sequences. One means for accomplishing this flexibility is to connect a variety of shift register logic elements to a given shift register by means of a crossbar or other complex switching network in order to develop a series of different non-linear feed forward generators which meet the criteria of the IEEE Transactions paper, supra. This sort of system suffers when high operating speed is necessary to system requirements. In this case, the complexity of the physical configuration limits system speed and the system becomes inoperable.
Another desirable feature of such a system would allow rapid switching from one complexity or sequence to another. Any switching system incorporating relatively long wire lengths, as in a crossbar switching network, would also be restrictive in terms of switching time due to excessive capacitive loading.
A system for meeting optimum system requirements clearly requires the following sub-requirements to be observed:
(1) A maximum number of multipliers must be available to the system, PA1 (2) Every span used in a given register complex must be unique, and PA1 (3) There must be no common connections in the register complex.